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What Causes Cancer?

Cancer is a renegade system of growth that originates within a patient's body. There are many different types of cancers, but all share one characteristic, unchecked cell growth that may progress toward limitless expansion.

The most important thing to remember is that cancer cells do not stop growing; soon the numbers become huge and a tumor can be seen, felt or detected. All of these cells have changes in their DNA or their surrounding tissue that cause them to behave in ways that are harmful. Normal cells know when to stop growing/dividing.

DNA damage or epigenetic changes have to occur before anyone gets cancer.


DNA Damage (For more complete information on all areas other than mutations and epigenetics, please go to Cancer 101 of our website)

DNA damage can be caused by the following factors:
  • DNA Mutations

  • Carcinogens

  • Lifestyle

  • Aging

  • Radiation

  • Infectious Agents

  • Epigenetic changes

  • Environment
Image courtesy of the National Cancer Institute

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Mutations make a person more susceptible to cancer

Aging, chemicals, lifestyle, environment and radiation act by: damaging genes

Viruses introduce their own genes into cells, sometimes causing cancer.

Other Infectious Agents cause inflammation and DNA changes that can potentially lead to cancer.



Mutations are errors in DNA structure that alter genetic information. To function correctly, each cell depends on thousands of proteins to do their jobs in the right places at the right times. Sometimes, gene mutations prevent one or more of these proteins from working properly. By changing a gene's instructions for making a protein, a mutation can cause the protein to malfunction or to be missing entirely. When a mutation alters a protein that plays a critical role in the body, it can disrupt normal development or cause a medical condition.

Mutations may be caused spontaneously by mistakes that occur during cell division, or they may be caused by exposure to DNA-damaging agents in the environment. Mutations can be harmful, beneficial, or have no effect. If they occur in cells that make eggs or sperm, they can be inherited; if mutations occur in other types of cells, they are not inherited. Certain mutations may lead to cancer or other diseases.

All mutations are changes in the normal base sequence of DNA. Many mutations are silent and have no effect.

This is because:

  1. We have a great deal of duplication in our genetic code

  2. We have repair mechanisms to fix errors

  3. Mutated cells are often unable to reproduce

However, when more and more mutations build up in a single cell, these mechanisms may not be sufficient to protect us from the uncontrolled reproduction that is characteristic of cancer.

One of the biggest problems with all of this genetic instability in cancer cells is that a tumor is likely to have several different genotypes amongst its many cells, which makes treatment difficult. Chemotherapy that's effective at treating cells with one sort of mutation may not be useful for another.

Image Courtesy of U.S. National Library of Medicine


There are two types of mutations

  1. Hereditary mutations: mutations passed on to us by our parents and present in all of our cells from birth. These are referred to as germ line mutations since they were present in the egg and/or sperm cells (called germ cells). Only about 10% of cancer is hereditary.

  2. Somatic mutations: are caused randomly during a lifetime of regenerating cells by:

    • Cell cycle errors

    • Copy errors during DNA replication

    • Environmental agents such as chemicals, smoking or pesticides

    • Radiation

    • Certain viruses

    • Other life style exposures
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